The present invention is directed to the replacement of the articulating surfaces of a knee joint in which the diseased area is restricted to either the medial or the lateral compartment, not both, and which still maintains good ligamentous stability. As compared to tricompartmental total knee arthroplasty, unicompartmental total knee arthroplasty, when its use is indicated, has a number of advantages. These advantages include less hospitalization, decreased blood loss, increased range of motion, and decreased pain.
Prior art workers have devised a number of procedures in unicompartmental total knee arthroplasty. The accuracy and reproducibility of the associated femoral and tibial cuts for preparation of the femur and tibia to receive their respective prostheses has long been a major concern to the orthopaedic surgeon. Prior art procedures and instruments require the serial fixation, removal and replacement of numerous cutting blocks to prepare the bone, basing secondary cuts on the not-so-inherent accuracy of the initial cuts.
The present invention is based upon the development of a method and instrumentation which allow the surgeon to complete all of the femoral and tibial cuts with one guide assembly for each. Both the femoral and the tibial guide assemblies are firmly affixed and are left intact until all the cuts have been completed, while still maintaining the versatility required for proper positioning.
The surgical procedure followed for preparing the distal femur bases the cuts on the affected condyle only, and does not disturb the unaffected side in any manner. Fixation of the single femoral cutting guide block is achieved utilizing the diseased side only.
The method and instrumentation of the present invention enables the use of a conventional femoral prosthesis having a pair of mounting pegs and a tibial prosthesis which comprises a tibial tray having anteriorly and posteriorly placed locking lips which engage the flexible tabs on the corresponding sides of a removable plastic bearing insert. The bearing insert is available in multiple thicknesses and both the tray and the insert are provided in left and right configurations. The tibial tray includes a rigidly affixed, posteriorly angled peg. According to the present invention, the tray also includes a medial and an anterior hole for screws by which it may be additionally affixed to the tibia. The posteriorly angled peg in conjunction with the screws provides divergent forces on the tibia to keep the tray firmly fixed. The femoral and tibial prostheses may also be affixed by an appropriate bone adhesive. The holes in the tibial tray for the mounting screws may be plugged with plastic inserts, when the mounting screws are not used.
In the preparation of the distal femur, a single cutting block is used. The cutting block is adjustable in the anterior-posterior plane and rotationally, and is firmly affixed to the femur by a femoral intramedullary rod on one side of the cutting block and an outrigger assembly on the other side of the cutting block, which is attached directly to the femur by a pair of smooth pins. The cutting block is provided with surgical saw guide slots for the posterior articular surface cut, the distal articular surface cut, and the chamfer cuts. All of these cuts are made with the single cutting block mounted in place. These four cuts can be made in any order. The cutting block can be used for resection of either the medial condylar surface or the lateral condylar surface by reversing the positions of the femoral intramedullary rod and the outrigger.
The surgical procedure followed for preparing the proximal tibia utilizes an intramedullary rod to which all components of the tibial cutting guide assembly are adjustably affixed. The tibial guide assembly includes a horizontal cutting guide which can be rotated about the intramedullary rod and shifted in all radial directions to facilitate proper positioning thereof against the anterior tibial surface on the operative side. The tibial guide assembly also includes a caliper measuring device to assist in the location of the horizontal cutting guide.
The tibial cutting guide assembly additionally includes a vertical cutting block, available in various widths, to guide the surgical saw during the vertical tibial cut.
The tibial cutting guide assembly for making both tibial plateau cuts can be used regardless of component sizing and with either compartment.